Offline-first is no longer a nice-to-have — it's an expectation. Users encounter poor connectivity constantly: elevators, subways, airplanes, rural areas, or simply overloaded networks at events. Apps that handle offline gracefully win user loyalty.
The offline-first philosophy: design your app to work offline by default, then sync when connectivity is available. This is the opposite of the traditional approach (assume online, degrade when offline) and produces fundamentally better user experiences.
Local-first data architecture is the foundation. Every piece of data the user needs is stored locally first (SQLite, Realm, WatermelonDB). The local database is the source of truth. Network requests sync changes in the background.
Conflict resolution is the hardest problem. When two users modify the same data offline and then sync, you need a strategy. Common approaches: Last-Write-Wins (simple but can lose data), Operational Transform (complex but preserves intent), and CRDTs (Conflict-free Replicated Data Types).
CRDTs have emerged as the preferred solution for many offline-first apps. Libraries like Yjs and Automerge implement CRDTs that automatically merge concurrent changes without conflicts. They're particularly powerful for collaborative features.
Queue-based sync is essential for actions. When a user performs an action offline (submit a form, like a post, place an order), queue it locally. When connectivity returns, process the queue in order. Show optimistic UI immediately.
Background sync APIs (iOS BGTaskScheduler, Android WorkManager) allow apps to sync data even when not in the foreground. Configure these carefully — respect battery life and data usage while keeping data fresh.
Testing offline scenarios requires discipline. Build toggle mechanisms to simulate various network conditions: full offline, slow 2G, intermittent connectivity. Test these scenarios as rigorously as you test normal operation.
Our offline-first architecture typically uses: WatermelonDB (fast SQLite-based local DB), custom sync engine with CRDT support, queue-based action processing, and React Native's NetInfo for connectivity monitoring. This stack handles 95% of offline-first requirements.